A compound of azetidinone has a structure of formula A as follows and a chemical name of (3R,4S)-4-(4-hydroxyphenyl)-3-[3-(4-fluorophenyl)-4-hydroxybut-2(Z)-enyl]-1-(4-fluorophenyl)-2-azetidinone. The compound of formula A is a novel plasma cholesterol reducing agent, which is used for reducing plasma cholesterol contents, thus being used for treating diseases highly correlated to the plasma cholesterol contents. WO2011017907 discloses a compound of formula A and preparation methods and applications thereof.

No report about the crystal forms of the compound of formula A is found at present. The inventor obtains the crystal forms of the compound of formula A through conducting a large number of experiments.